Feline caliciviruses (FCV) were first described in 1957 (Fastier L. B. Am. J. Vet. Res. 1957. 18, 382-389). Feline caliciviruses are, with the feline herpesviruses, the two principal sources of viral diseases of the upper respiratory tract in cats. The FCV viruses affect a large number of animals, with FCV carrying rates of the order of 15 to 25%, and an anti-FCV seroprevalence of 70 to 100% (Coutts et al. Vet. Rec. 1994. 135. 555-556; Ellis T. M. Australian Vet. J. 1981. 57. 115-118; Harbour et al. Vet. Rec. 1991. 128. 77-80; Reubel et al. Feline Dendistry 1992. 22. 1347-1360). After an initial phase of hyperthermia, these respiratory diseases are generally accompanied by buccal ulcerations (palate, tongue, lips, nose), rhinitis, conjunctivitis, possibly anorexia and asthenia. The FCV viruses can also cause pneumonia, enteritis, and articular pain (lameness syndrome).
The FCV virus is transmitted only horizontally, there is no vertical transmission from the mother to its kitten during gestation (Johnson R. P. Res. Vet. Sci. 1984. 31. 114-119). FCV is transmitted by contact between infected animals and healthy animals or by the airways during sneezing (Wardley RC. Arch. Virol. 1976. 52. 243-249).
Feline caliciviruses are naked viruses of the Caliciviridae family; they possess a single-stranded positive RNA of about 7.7 kilobase pairs (kbp) in size (Carter M. J. Arch. Virol. 1994. 9. 429-439).
Like many RNA viruses, a large heterogeneity exists within the viral population of FCV. The antigenic variations, demonstrated since the beginning of the 70s by cross-serum neutralization experiments, make it possible to classify the FCVs into several viral strains or quasispecies (Radfoord et al. Proc. 1st Int. Symp. Caliciviruses ESVV 1997. 93-99).
Several FCV strains have been isolated and sequenced, in particular the strain F9 (Carter et al. Arch. Virol. 1992. 122. 223-235, sequence deposited in the GenBank databank under the accession number M86379), FCI (Neill et al. J. Virol. 1991. 65. 5440-5447, GenBank accession number U13992 and M32819), Urbana or URB (Sosnovtsev and Green Virology 1995. 210. 383-390, GenBank accession number L40021), F4 (Tohya et al. Arch. Virol. 1991. 117. 173-181, GenBank accession numbers D31836 and D90357), KCD (Fastier L. B. Am. J. Vet. Res. 1957. 18. 882-889, GenBank accession number L09719), LLK (GenBank accession number U07131), NADC (GenBank accession number L09718), 2280 (GenBank accession number X99445) and 255 (Kahn and Gillepsie. Cornell Vet. 1970. 60. 669-683, GenBank accession number U07130).
Vaccination against FCV was introduced since the end of the 70s from attenuated FCV strains, mainly strain F9 isolated in 1958 by Bittle (Bittle et al. Am. J. Vet. Res. 1960. 21. 547-550) or strains derived from F9 by passage in vitro or in vivo (“F9-like”).
Inactivated vaccines are also available. They use strains 255 and 2280, which were isolated respectively in 1970 in a cat with a pneumonia (Kahn and Gillepsie. Cornell Vet. 1970. 60. 669-683) and in 1983 in a cat suffering from lameness (Pedersen et al. Fel. Prac. 1983. 13. 26-35).
The humoral response is essentially directed against the capsid protein, also called p65 (Guiver et al. J. Gen. Virol. 1992. 73. 2429-2433). The genes encoding the capsid protein of many feline caliciviruses have been sequenced and compared without it being possible to distinguish more clearly certain sequences (Glenn et al. Proc. 1st Int. Symp. Caliciviruses ESVV 1997. 106-110; Geissler et al. Virus Res. 1997. 48. 193-206; Neill et al. Proc. 1st Int. Symp. Caliciviruses ESVV 1997. 120-124).
The gene encoding the capsid protein has also been cloned and expressed in various expression systems, in particular the gene encoding the capsid protein of the KS20 FCV virus in plasmids (Geissler et al. J. Virol. 1999. 73. 834-838), the genes encoding the capsid proteins of the CFI-68, JOK63, JOK92, LS012 and F9 FCV viruses in baculoviruses (DeSilver et al. Proc. 1st Int. Symp. Caliciviruses ESVV 1997. 131-143), the gene encoding the capsid protein of the F4 FCV virus in type 1 feline herpesviruses (Yokoyama et al. J. Vet. Med. Sci. 1998. 60. 717-723). These various constructs have allowed the production of recombinant capsid proteins.
Because of antigenic drift over time, antisera produced against old vaccine strains isolated in the 60-70s, such as strains F9, 255 or 2280, neutralize only few isolates of the 90s. For example, the anti-F9 serum neutralizes 43% of the isolates of the period 1990-1996, against 56% for the period 1980-89 and 86% for the period 1958-79, and only 10% of the English isolates of the period 1990-96 (Lauritzen et al. Vet. Microbiol. 1997. 56. 55-63).
The objective of the present invention is the detection of FCV strains, which induce in cats antibodies against a broad cross-neutralization spectrum.